U.S. officials say no additional testing is needed to prove the existence of harmful interference

A recent government study found that the LightSquared Inc. wireless service interrupted 75 percent of global-positioning system (GPS) receivers.

LightSquared Inc. is a company looking to offer a wholesale 4G LTE wireless broadband communications network with satellite coverage in the United States. It was founded by Philip Falcone and has had interference issues for years now. Just this year alone, interference concerns were raised by the National Telecommunications and Information Administration (NTIA), USAF Space Command, and the U.S. GPS Industry Council.

Now, a test conducted by the U.S. government has shown that 69 of 92 (75 percent) of receivers experienced "harmful interference" at the equivalent of 100 meters from a LightSquared base station. It was deemed that millions of GPS units were incompatible with the LightSquared service, and it could affect cars, planes, boats and tractors.

The test was performed from October 31 to November 4 for the National Space-Based Positioning, Navigation and Timing (PNT) Systems Engineering Forum, which advises policy makers about GPS issues. The Department of Defense and the Federal Aviation Administration took part in the testing, as well as companies like Garmin Ltd., Trimble Navigation Ltd., Deere & Co., and General Motor Co.'s OnStar unit.

"LightSquared signals caused harmful interference to majority of GPS receivers tested," said U.S. officials in a draft prepared for the review of the LightSquared proposal. "No additional testing is required to confirm harmful interference exists."

LightSquared has proposed that it operate at a reduced power than the levels used during the testing. With low power usage, LightSquared believes its services would only affect 10 percent of devices.

Well I was just wondering about that spectrum...I know nothing about this other than the article above, but I am left to wonder why the spectrum they bought would have such obvious interference problems with another existing service. Did somebody screw up on the spectrum that these guys got, or what?

They have to be leaking outside what they were given, there's no way they were licensed on the same frequencies that GPS uses. Someone skimped on their filter design and it they are leaking more than they should into neighboring bands. Most likely it would usually be fine, but GPS is such a low power signal that it's easy to interfere with.

The GPS receiver folks are the ones who skimped on their filter designs, and now they're claiming their installed base is so large that Lightspeed shouldn't be allowed to go forward. The truth is, they should have to meet THEIR frequency constraints to not be interfered with by Lightspeed.

This is like 1915 Ford saying "OOPS, we made the Model T too wide for the road, but now that there's so many of them we can't/won't share the road with any other vehicles." Lightspeed wants to build motorcycles, but Ford says all they can build are bicycles and they should stick to the sidewalk.

They did not skimp on the filter designs. LightSquared's spectrum was original allocated for satellite communications. That's what the FCC told everyone the spectrum would be used for, and what the GPS receivers were designed to filter out. Nearly undetectable satellite signals raining down and the occasional satellite dish aimed straight up; not towers every 15 miles blasting away in all directions.

To use your analogy, it's like Ford making cars that fit four abreast on the road. There's also a bike lane on the roads, and LightSquared bought a license to operate bikes in that bike lane. But by asking "nicely", they got the government to approve of them hauling oil tankers down the bike lane.

A similar fence was implemented by allowing directional broadcast to satellites in orbit & low power broadcast to Earth based receivers. In that application, at the power levels allowed, the sideband noise was being filtered out by the GPS equipment. Unfortunately for Lightspeed, the FCC did not eliminate the sideband noise when they changed the permitted usage. Physics tends to trump bribes no matter what the lobbyists may try to tell you.

Increased broadcast power==increased sideband noise. Existing GPS equipment was designed to ignore the legally allowed noise from neighboring bands. The FCC now needs to modify the GPS license to increase the amount of noise they are required to tolerate or disallow this version of 4G cellphone service on these specific frequencies.

The problem isn't the spectrum, it's the GPS receivers. Because GPS signals are so low power, you don't want any attenuation of the signal. Really good sharp filtering is expensive, so many cheap receivers don't have much filtering for out of band signals, and are susceptible to interference. Even good receivers can have issues.

From what I remember, there were arguments about this, from the Air Force and IEEE, before Lightsquared was even sold the spectrum. The FCC still sold it to them, claiming the low power function would not cause problems. This is the same low power functionality they claim will not cause problems now, even though they had the test equipment set to run in high power mode by default.